The invention relates to an oscillating-piston engine, comprising a housing, in which several pistons configured as two-armed levers are arranged pivotably, respectively, around a pivot axis being parallel to a central housing axis and are movable commonly in a revolution direction, wherein the pistons have running surfaces on their side facing away from a housing inner wall, the running surfaces when the pistons revolve in the housing, being guided alongside of at least one control cam of a central housing-fixed cam piece, in order to control the pivot movements of the pistons in revolution.
Such a oscillating-piston engine is known from WO 98/13583, the disclosure of which is herewith explicitly included into the present application.
Oscillating piston-engines belong to a type of internal combustion engines, in which the single working strokes of intake, compression, ignition (expanding) and expulsion of the combustion mixture are mediated by rock-like pivot movements of the single pistons between two end positions.
The known oscillating piston-engine has centrally in the housing a housing-fixed cam piece, which comprises an outer contour configured as a control cam. The pistons have running surfaces on their sides facing away from the housing inner wall, i.e. on their sides facing the central cam piece, the running surfaces being guided, when the pistons revolve in the housing alongside the outer contour of the cam piece, in steady contact with same. The pivot movements of the pistons are controlled in this procedure, when the pistons revolve in the housing, by the guiding of the running surfaces of the pistons alongside the outer contour of the cam piece in combination with a rolling engagement of respectively adjacent pistons.
Although the known oscillating piston-engine has turned out to be particularly favorable for what concerns its running characteristics, it can be improved for what concerns its wear-resistance and fail-safety, in particular in long-term operation and in high performance operation.
Calculations with respect to kinematics of the known oscillating piston-engine have, namely, shown that the centrifugal forces of the oscillating pistons adopt different values between a minimum and a maximum, seen via a full revolution in dependence of the momentous rotation position, which is to be explained by the asymmetric mass position of the oscillating pistons with respect to the center of the pivot axes of the single pistons.
The maximal centrifugal force occurs in each piston when it is in the so-called Upper-Dead-Center (TO) position (12 o""clock position) or in the Bottom-Dead-Center (UT) position (6 o""clock position). This maximal centrifugal force acting on the leading lever arm of the piston being in the TO position, which presses this lever arm to the outward into the direction of the housing inner wall, results in a force of equal amount directed to the cam piece acting on the trailing lever arm of the same piston. As this trailing lever arm is in rolling engagement with the leading lever arm of the next trailing piston, the trailing lever arm of the leading piston presses the leading lever arm and, thus, the running surface arranged on that lever arm with increased force against the cam piece. This is because only a centrifugal force minimum acts upon on the leading lever arm of the trailing piston, which is just in the drawn-in 9 o""clock position or 3 o""clock position, so that this minimal centrifugal force does not compensate the compressive force caused by the centrifugal force in the TO position. The consequence is that the running surface of the trailing piston in the 9 o""clock position or of the piston in the 3 o""clock position is pressed against the cam piece with very high force, whereby both the running surface and the cam piece are excessively loaded.
In long-term operation, this may result in increased wear or even in damage of these parts, in particular when the rotational speed is high and, therefore, the centrifugal forces are high.
It can be seen from the above that the teething of the rolling engagement, which has to absorb opposing forces, is even more force loaded.
Moreover, a centrifugal piston combustion engine is known from DE-OS-15 51 101, which comprises six pistons of an approximately triangle form distanced from each other, which are mounted, pivotably, on a circle-shaped driving wheel such that they are pressed against the inner wall of the housing by the occurring centrifugal forces, when rotating in the housing of the engine. The control of the pivot movement of the single pistons is, in this procedure, caused by a special trochoid-shaped embodiment of the housing inner wall. In the housing, moreover, two stationary guiding cams with an outer contour are arranged, which are to guarantee, at low speed of the engine, when the centrifugal forces are low, that the pistons are pressed against the inner wall of the housing to guarantee working of the engine, when the speed is low. This centrifugal piston engine is disadvantageous, however, already because of the required special noncircular contour of the housing inner wall.
From DE-OS-15 26 408, a combustion engine with revolving pistons which form a closed chain is further known. The pistons form, together with the noncircular, approximately oval cylinder jacket, closed rotating working chambers of changeable volume. The articulation polygon formed by the pistons is a pentagon or a polygon, whereby a regular pentagon is considered as to be the most advantageous. For the control of the piston movement, two auxiliary rotors are provided, which consist of five segments, these segments being articulatedly connected via bolts. On the bolts, rollers are mounted, which, rolling over the race, control the movement of the rotors and by means of further bolts the movement of the pistons, too. This embodiment of an oscillating-piston engine is relatively expensive. Further disadvantages of this embodiment are the noncircular configuration of the housing inner wall and the articulated connection of the segments forming the two auxiliary rotors for controlling the pivot movement of the pistons.
From U.S. Pat. No. 3,642,391, another oscillating-piston engine is known, in which the pistons are in pairs articulatedly connected to each other. The form of the housing inner wall of this oscillating-piston engine is not round, but elliptical. The piston pivot movements are controlled by cam pieces, on which the pistons run with rollers. Also in this oscillating-piston engine, the noncircular contour of the housing inner wall is disadvantageous.
It is therefore an object of the invention to improve an oscillating-piston engine mentioned at the outset in such a way that the disadvantages mentioned before are avoided. The oscillating-piston engine is to be improved with reference to its wear characteristics and fail-safety.
According to the invention, this object is achieved by an oscillating piston engine, comprising:
a housing having a central housing axis and a housing inner wall;
several pistons configured as two-armed levers, said pistons being arranged in said housing and moving/orbiting together in a revolution direction about said central housing axis;
several pivot axes parallel to said housing axis, each of said pistons arranged pivotably about one of said pivot axes, respectively;
a stationary cam piece with respect to said housing and arranged centrally in said housing, said cam piece having an outer contour and at least one inner contour, said outer contour and said inner contour being configured as control cams, wherein said pistons have, at a side facing away from said housing inner wall, running surfaces,
which are guided alongside said inner contour supportedly to a side of a centrifugal force and alongside said outer contour supportedly into a direction of the housing axis, in order to control pivot movements of said pistons in the revolution about said central housing axis.
The oscillating-piston engine of the invention, thus, further assumes that the pivot movements of the single pistons when revolving are controlled by a housing-fixed central cam piece, which has proved to be advantageous compared to the known centrifugal piston combustion engine. In the oscillating-piston engine, however, in form of the control cam configured as inner contour, alongside of which the running surfaces of the pistons are guided, a measure has been taken in order to absorb the centrifugal forces of the piston halves or lever arms of the pistons. As the control cam configured as inner contour absorbs the centrifugal forces, it is avoided that the centrifugal forces, in particular the maximal centrifugal forces occurring in the TO position, are transmitted, over the rolling engagement onto the running surface or running surfaces of the respective leading and trailing piston and onto the cam piece. In this way, overload of the running surfaces and of the cam piece is avoided. Another advantage resulting from the embodiment of the cam piece according to the invention is that also the forces in the region of a rolling engagement between adjacent pistons, if such a rolling engagement exists, are also reduced in an advantageous manner.
The cam piece further has another outer contour configured as control cam, alongside of which the same running surfaces or other running surfaces of the pistons, the running surfaces being also arranged on the side facing away from the housing inner wall on the pistons, are guided supported into the direction of the housing axis.
In this measure, each piston experiences both an xe2x80x9couter guidingxe2x80x9d alongside of the known per se outer contour and, additionally, an xe2x80x9cinner guidingxe2x80x9d alongside the inner contour of the cam piece. Such a combination of inner guiding and outer guiding allows a kinematically exact and, at the same time, a dynamically favorable control of the pivot movements of the pistons when rotating in the housing, whereby reaching the important advantage that the running surfaces in the position 9 o""clock and 3 o""clock are compression relieved in comparison to the known oscillating-piston engine. Another advantage of the combination of an inner guiding and an outer guiding is that in a rolling engagement of respective adjacent pistons this rolling engagement has essentially no control function any more, but has merely the function of a sealing. This offers the possibility to configure the rolling engagement in form of a smooth rolling surface instead in form of a teething, or even omit a rolling engagement, as is provided in a preferred embodiment.
In a preferred embodiment, the outer contour and the inner contour run parallel to each other.
In this embodiment, the inner contour and the outer contour have curve courses essentially complementary to each other. Each piston is, thus, guided both centrifugally and centripetally, like on a rail. The embodiment of the inner contour being parallel to the outer contour has the advantage that it is possible to modify with simple means the oscillating-piston engine known and proven from WO 98/13583 according to the present invention. For example, the piston geometry and the geometry of the outer contour of the cam piece can be kept essentially unchanged, whereby, then, merely on the cam piece an inner guiding surface for the pistons needs to be provided.
In another preferred embodiment, the inner contour is configured continuous in revolution direction.
It is here of advantage that each piston is supported over a full revolution to the side of the centrifugal force, i.e. centrifugally, so that in each rotation position of the pistons centrifugal forces are absorbed and, thus, compression stress is reduced in each rotation position.
Alternatively it is also preferred, however, in the case of an embodiment with an inner contour and an outer contour if the inner contour extends only over one or more circumferential sections in the revolution direction.
In this way, a simpler configuration of the oscillating-piston engine can be reached, whereby it is preferred in this case, if the inner contour extends at least in the region of the Upper-Dead-Center and of the Bottom-Dead-Center, for instance, from 10 o""clock until 2 o""clock and from 4 o""clock to 8 o""clock.
In another preferred embodiment, the cam piece has the outer contour and the at least one inner contour in a one-piece configuration.
In this embodiment, the cam piece can be, altogether, in one piece, whereby the manufacturing costs and the number of the parts entering the construction can be reduced. Proceeding from the cam piece of the known oscillating-piston engine, the inner contour provided according to the invention can be formed in the manufacture of the cam piece. Another advantage of a one-piece configuration of the outer contour and the inner contour is that a stable orientation of the two contours is guaranteed in the long run during the operation of the oscillating-piston engine.
Alternatively to that embodiment, it is also preferred, however, to have the cam piece configured in several parts, wherein at least a first part has the control cam configured as outer contour and at least a second part has the at least one control cam configured as inner contour, and the parts are firmly connected to each other.
This embodiment proves to be advantageous because of facilitated mounting when joining the running surfaces of the pistons with the cam piece. The inner contour can here be configured on a ring flange which is flanged onto the remaining cam piece comprising the outer contour.
In another preferred embodiment, the inner contour is arranged on an inner side of bag-like flanges of the cam piece.
This measure is particularly advantageous both from the manufacture point of view and of the mounting point of view. If the cam piece comprises both the inner contour and the outer contour, the flange or the flanges can be configured in one piece with the other part of the cam piece comprising the outer contour, or as separate ring flanges, which are, then, connected positively to the other part of the cam piece comprising the outer contour, the positive connection being, for instance, a connection by pins. The bag-like flanges form an approximately reversed L-shaped overlapping of these running surfaces, which are provided for the guiding at the inner contour.
In another preferred embodiment, the cam piece has, in the region of both axial ends of the pistons, respectively, axially limited, the inner contour.
In this embodiment, each piston is, thus, guided with its both axial ends on the side of the centrifugal force. The axially central region of each piston can, then, if provided, have the running surfaces, which are radially guided, at the outer contour, supported to the inner side.
If the cam piece comprises both the inner contour and the outer contour, it is further preferred, if each piston comprises at least two running surfaces, at least one of which is guided at the inner contour, while the at least one further running surface is guided at the outer contour.
This embodiment offers advantageously the possibility to realize the running surfaces by rollers, whereby, then, the at least one roller being guided alongside the inner contour can freely roll on the inner contour and the at least one roller being guided at the outer contour can also freely roll on the outer contour.
In another preferred embodiment, the running surfaces are surfaces of rollers being rotatably mounted on the pistons.
Rollers have the advantage that they can be guided with an essentially less friction alongside the inner contour and/or alongside the outer contour of the cam piece. The demands on the lubrication of the running surfaces can be considerably reduced in comparison to piston-fixed slide shoes.
In another preferred embodiment, the pistons are, respectively in pairs, in rolling engagement with each other.
This measure is advantageous in the case that the pistons are guided only alongside the inner contour, but, however, not alongside the outer contour, so that the rolling engagement can, then, take over an additional control function for the to and fro pivot movement of the pistons.
In another preferred embodiment, the pistons are, respectively in pairs, in rolling engagement with each other via an unteethed curved rolling surface.
As already mentioned before, the forces are reduced in the region of the rolling engagement of adjacent pistons by the guiding of the pistons according to the invention alongside the inner contour and even stronger in an additional guiding of the pistons alongside the outer contour, so that the rolling engagement has mainly a sealing function. According to that, the rolling engagement can also be represented as a smooth rolling surface, which is easier to manufacture than a teething.
Alternative to a rolling engagement of respectively adjacent pistons, it is equally preferred if the pistons, seen in circumferential direction, are spaced, respectively, in pairs via a respective dividing element, wherein the dividing elements revolve together with the pistons in the housing.
This embodiment is in particular in an advantageous way possible, when the pivot movement of the single pistons is both performed via the inner outer guiding and via the outer inner guiding of the cam piece. The single pistons are, then, because of the no more existing rolling engagement, completely independent of each other, with the advantage that at the surface between piston and dividing element in a constructively simple manner seals of common type can be used.
In this measure, it is further preferred if each dividing element has two sliding surfaces, on which piston fist surfaces of the two respective corresponding pistons being in contact with the respective dividing element slide to and fro during their pivot movement.
The dividing elements are, thus, preferably stationary with respect to the pivot movement of the pistons, and revolve merely with the pistons in the housing in the revolution direction.
The dividing elements can be firmly clamped between two annular elements moving with the pistons at the respective end face of the oscillating-piston engine.
The piston fist surfaces of the pistons can be configured e.g. in a convex fashion and the sliding surfaces of the dividing elements can be configured in a concave fashion, or vice versa. Such a curved forming of the piston fist surfaces and sliding surfaces sliding in contact with each other is optimally adjusted to the pivot movement moving to and fro of the single pistons. The complementary forming of the piston fist surfaces and of the sliding surfaces further allow an optimal sealing of the work chambers against the oil space of the oscillating-piston engine via the whole pivot stroke, if the dividing elements extend, in axial direction, over the length of the interior of the housing of the oscillating-piston engine.
In this measure, it is preferably provided to arrange at least one seal in each sliding surface of the dividing elements, respectively.
Such sealings can be provided in the form of sealing lips, which are arranged in the same place where the corresponding sealing lips are arranged next in the ring sides at the face of the piston cage of the longitudinal central axis of the oscillating-piston engine.
The arrangement of the seals in the dividing elements is, however, not imperative, the seals may as well be arranged in the piston fist surfaces of the pistons instead of in the dividing elements.
In another preferred embodiment, in each sliding surface a fire seal nearer to the housing inner wall and an oil seal nearer to the cam piece is arranged.
The fire seal seals gas-tight the work chambers, where the combustion process takes place, while the oil space arranged centrally in the oscillating-piston engine is additionally sealed via the oil seal against the work chambers.
In another preferred embodiment, the oscillating-piston engine has several chambers in axial direction, wherein in each chamber a set of pistons is arranged, and wherein the sets of pistons are displaced to each other from chamber to chamber in circumferential direction.
While the known oscillating-piston engine is configured as one-chamber-system in axial direction, the multi-chamber embodiment has the advantage that the torques passed by the piston onto the cam piece can be halved or divided into thirds or divided even further, corresponding to the number of the chambers because the torque-effective surface of the pistons can be configured correspondingly smaller in axial direction. By displacing the piston sets from one chamber to the next chamber, the torque transmission onto the central cam piece is more regularly distributed in circumferential direction. In that way, the smoothness of running of the oscillating-piston engine can be increased in an advantageous way, and the load of the cam piece, which can be configured continuous through all chambers in one piece or in several parts, can further be reduced.
Further advantages can be taken from the description and the enclosed drawings.
It is to be understood that the features mentioned above and those yet to be explained below can be used not only in the respective combinations indicated, but also in other combinations or in isolation, without leaving the scope of the present invention.